Effect of dopant solubility and excess doping on the superconducting properties of doped Nb3Sn prepared by field assisted sintering technique.

The present work is focused on understanding the role of Ruthenium (Ru) and Yttrium (Y) on the superconducting properties of the A15 Nb 3 Sn intermetallic compound. Ru and Y shows different solubility limit within the Nb 3 Sn matrix. Ru and Y-doped Nb 3 Sn superconducting alloys were prepared through mechanical alloying (MA) route followed by sintering using Field Assisted Sintering Technique (FAST). Analysis by X-ray diffraction demonstrates a significant decrement in crystallite size up to 0.5 wt% for the Ru-doped Nb 3 Sn followed by a significant increment when doping level reaches 1 wt% Ru. This could be the combined effect of structural disorderliness and Ru dissolution within the Nb 3 Sn matrix. While a significant increase in the crystallite size is observed for 0.5 wt% Y-doped Nb 3 Sn and no further change up to 1 wt% Y. This change could be a result of limited solubility of Y within the Nb 3 Sn matrix. Meanwhile, excessive Y plays an important role in the formation of additional flux pinning centers. The critical current density (J c) shows a significant increase for all the Y-doped Nb 3 Sn alloys by a factor of 29 % due to the formation of Y 2 O 3 from the residual Y, which is assumed to serve as additional flux pinning center. The Y 2 O 3 particles was also considered as a possible cause of pinning down of grain boundaries in addition to NbO leading to grain refinement through Zener pinning. Ru-doped Nb 3 Sn alloys also exhibit an increase in J c compared to pristine Nb 3 Sn, but only in concentrations up to 0.5 wt% Ru. At higher applied field, even 1 wt% Ru shows slight increase in J c than pristine Nb 3 Sn. Y-doped samples showed superior functional properties. • The concentration of dopants in Nb3Sn plays a crucial role in defining its functional properties. • The solubility limit of dopants has significant effects on superconducting properties of Nb3Sn. • Yttrium (Y) with limited solubility enhances superconductivity while Ruthenium (Ru) does the opposite. • Formation of additional flux pinning centers led to higher functional behaviour for Y modified Nb3Sn. [ABSTRACT FROM AUTHOR]